The purpose of this project is to develop methods for the extraction, isolation, and characterization of polypeptides with the property of conferring the transformed phenotype on normal indicator cells. These purified transforming growth factors (TGF's) will then form the basis for investigation of the mechanism of transformation and, more specifically, for the development of protein antagonists to these TGF's. Central to the investigation is the purification and characterization of the TGF's found in chicken cells transformed by Rous sarcoma virus. Such tissues are obtained from birds inoculated with RSV or from cells transformed by the virus in culture. TGF's have also been obtained from normal chick embryos.